Mammal Species of the World's Boreal Forests


Rattus norvegicus
Norway Rat
"Brown Rat" or "Common Rat"


Norway Rat Distinguishing Features - Total length, 440 mm; tail 205 mm. Weight: 400 - 500 g. The Norway rat is a coarse-furred rat with prominent, naked ears and nearly naked scaly tail which is shorter than the head and body. Molars of the upper jaw have tubercles in three longitudinal rows, as in the house mouse. General color above is brown/dark gray with scattered black hairs, while underparts are pale gray or grayish brown; may also be gray, white, black, or two-coloured as in the photo illustration below. Laboratory rats are domesticated albino strains of the Norway rat.

Norway Rat Habitat

This cosmopolitan rat originated in northern China and has spread to nearly every part of the world as stow-aways aboard ships. As elsewhere, in Scandinavia and western Russia, it is encountered in areas around human settlement, and wherever there is an abundance of food and shelter - from the subways and crowded tenements of metropolitan districts, to the corn and grain fields of farm country.


The Norway rat is a true omnivore; it shuns few items. It eats everything from soap to candy, milk, meat, vegetables, poultry, eggs and all grains, nuts and fruits. Its appetite is prodigious: it can eat a third of its weight in twenty-four hours. Norway rats are also capable of catching fish and small rodents, and they readily eat carrion. In cities, this rodent thrives on the uneaten and spoiled food constantly discarded by humans. Their main constraint is that they cannot go long without water unless their diet contains other liquids in adequate amounts.


Norway rats are prolific breeders. The gestation period varies from 21 to 23 days and the number of young from two to 14, averaging seven or eight. At birth they are blind, naked, and helpless. They grow rapidly; their eyes open in 14-17 days and they are weaned when 3 or 4 weeks old. There is no delimited breeding season, but there is a tendency for a slow-up in reproduction during fall and winter. The life span is reported to be 2-3 years.

Black Rat The species is sometimes confused with the Black rat (Ship rat) Rattus rattus (pictured to the right) which is slightly smaller and less aggressive. In the boreal regions, the range of the Norway rat extends into colder northern latitudes.

Although both species are preyed upon by a number of animals, predators often are not able to keep the rat population in check. Considerable destruction of property and foodstuffs can take place where rats are abundant. In addition, they constitute a menace to public health. They are known to be reservoirs of bubonic plague (transmitted to man by the bite of a flea or other insect), endemic typhus fever, ratbite fever, and a few other dreaded diseases. Because of this it is commonly said that Norway and Black rats are more dangerous than lions or tigers.

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